The present invention relates to a catalyst for decomposing and removing ozone contained in gas or the like.
Examples of a conventional method for removing the harmful ozone contained in the gas, include (i) an adsorbing method using a porous substance such as a catalytic active substance or ozone adsorption substance, zeolite or the like and (ii) an oxidizing and decomposing method using a catalyst such as MnO.sub.2.
However, none of the conventional decomposing methods above mentioned fully achieve a satisfactory decomposition. More specifically, in the adsorbing method, the adsorbent needs to be regenerated or exchanged since its adsorbing ability expires in a limited period of time. This presents the problem that a removing apparatus requires much labor and expense for maintenance.
The oxidizing and decomposing method using a catalyst includes no such problems as above mentioned, but does not fully achieve satisfactory decomposition in view of catalyst performance. In addition, the performance is initially good but deteriorates with the passage of time during reaction.
The present inventors have variously investigated the reaction for oxidizing and decomposing ozone. As a result, the following has been found. In other words, since the rate determining step of the reaction is the step of diffusion into the solid, the reaction proceeds only on the catalyst surface. Consequently, it is most preferable that the catalytic composition is of the coating-type in which catalytic active components are carried on the catalytic surface and in the vicinity thereof. However, in the case where a honeycomb construction is used for a carrier, cells of the honeycomb are easily plugged by the coated catalytic active components and the ease of plugging increases as the number of cells/inch.sup.2 is increased. Consequently, there is caused the problem that a low-pitch honeycomb type catalyst for decomposing ozone, which has great number of cells/inch.sup.2, is poor in productivity.
Accordingly, it is a main object of the present invention to provide a catalyst for decomposing ozone which is superior to the conventional catalyst in its ability to remove ozone by an oxidizing and decomposing method.
It is another object of the present invention to provide a catalyst for decomposing ozone which has good durability for a long time.
It is yet another object of the present invention to provide a catalyst for decomposing ozone having high productivity even if the carrier therefore is a low pitch honeycomb-type.